Lithium/thionyl chloride (Li/SOCl 2 ) batteries are considered as promising power sources because of their high energy density, high operation voltage, long storage life and wide operation temperature range. In this thesis, poly(vinylpyrrolidone) or PVP was introduced as an option for improving lithium thionyl chloride battery performance and reduce the amount of lithium chloride insulating layer formed on the carbon cathode. In fact, this polymer by linking with the lithium ions from the lithium electrode oxidation, preventing them from reaching chloride and precipitate them on the carbon surface. The effect of PVP in three-electrode system and battery have been investigated. The electrochemical behavior of this polymer in the electrolyte and carbon paste was investigated using cyclic voltammetry, linear sweep voltametery and chronoamperometry techniques. The CV data as depicted clearly show that the reduction peak has more than doubled the amount of current and more positive potential start in the presence of PVP in the electrolyte. Also, the activity and stability in the presence of PVP in the electrolyte are higher. Structure of the layer formed on the carbon electrode surface examined using scanning electron microscopy that shows the carbon covered by a lower level of insulation layer of lithium chloride, when the PVP is in the electrolyte. The electrochemical experiments in the presence or absence of PVP in the electrolyte in the battery, includes polarization curves and electrochemical impedance spectroscopy. The results of battery are in agreemment with three electrodes data and showing that the discharge potential is higher and more uniform in the presence of PVP in the battery electrolyte. The polarization curves also show that the presence of the polymer causes the concentration polarization of the battery is being less and therefore has a higher potential. These results are agreement with the results of the electrochemical impedance. Then, the polarization curves and electrochemical impedance spectrum were recorded for number of commercial Li/SOCl 2 , “D” size, bobbin structure with Different duration of using. The results show that with increasing duration of use and formation of denser and thicker lithium chloride on the carbon cathode battery, polarization increases in the mass transfer. more mass and charge transfer resistance with increasing duration of use of the battery in the impedance spectrum of batteries is also significant.